Security systems for protecting of property, in particular homes, have become quite common as well as the monitoring of such systems by a central monitoring service. Initially, these security systems were hard wired systems where the various sensors and data entry keypads were hard-wired to a control panel. The control panel processed all the information and based on this information, determined alarm conditions and preferably completed a telephone communication with a central monitoring service.
As the systems continued to develop, the sensors for detecting motion and/or the state of windows or doors, communicated with the control panel by a narrow band RF transmission and as such, were wireless. Most of these systems continued to have a keypad typically adjacent a particular entry point, which keypad was used by the owner to arm the security system and disarm it when he returned to the premises. The keypad was hard-wired to the control panel and basically functioned as a dumb terminal.
Some security systems have used a one-way narrow band RF keypad where each keypad entry is transmitted to the control panel using an RF transmitter. These keypads do not have a receiver and therefore only send information to the control panel as it is entered at the keypad. Such one-way systems have limited usefulness as they cannot provide confirmed information as to the status of the system and cannot allow the user to query the control panel for system information. In addition to facing limitations imposed by FCC and other broadcasting authorities on narrow band RF systems, excessive RF transmissions of such one-way systems can also cause control panel problems. The control panel can only receive one signal at a time and transmission of multiple signals can corrupt or block transmissions. Various arrangements have been used to reduce the impact of this problem. Some of the solutions included multiple signal transmissions at spaced time intervals designed to minimize the likelihood of conflict, however, this may unnecessarily increase the traffic. The prior art one-way keypads typically transmitted in the 300 MHz band, which must meet strict FCC regulations, which limit their effectiveness. There was also problems with expected battery life and there was no check on the integrity of the system, as the keypad was basically blind to the control panel and other components.
For these reasons, hard-wired keypads are most commonly used.